1. Field of the Invention
The present invention relates to reliability metrics for communication networks, and specifically to defining and determining end-to-end reliability metrics for such networks and a service offered over such networks.
2. Brief Discussion of Related Art
Availability estimation in a public switched telephone network (PSTN) typically relies on the concept of a reference connection. The reference connection usually consists of a single path through the PSTN from one end user to another, including the major network segments needed to connect two telephone subscribers served by two different central office switches. A static allocation of end-to-end objectives to different network segments is used to meet specific availability requirements. This conventional approach is often used for availability standards.
Typically the level of availability is defined in a customer service agreement, where the service provider agrees to maintain the availability at the specified level. For example, in such an agreement, five-9 availability or 99.999% availability is defined as the level of availability to be provided. Availability is typically a time average measure based on an amount of time that a reference connection or a specified part of the network is unavailable for some specified time period.
In reality, end-to-end availability can vary significantly among different end points. For IP networks, a model of an end-to-end reference path between provider-edge (PE) routers and an associated reliability model can be developed. However, IP application flows can take different paths within the network and the reference connection typically provides the availability of one route between a pair of PE routers in the core IP network with the assumption that all routes, or at least a large fraction of them, have a similar availability. These considerations render the concept of a reference connection less effective for IP networks.